TECHNICAL FIELD
[0001] The present invention relates to an exhaust gas purification system for an internal
combustion engine which is provided with an exhaust gas purification device that is
arranged in an exhaust passage of the internal combustion engine and is constructed
to include a catalyst, and a precatalyst that has an oxidation function and is arranged
in the exhaust passage at a location upstream of the exhaust gas purification device.
BACKGROUND ART
[0002] In case where an exhaust gas purification device constructed to include a catalyst
is arranged in an exhaust passage, a precatalyst having an oxidation function may
be arranged in an exhaust passage at a location upstream of the exhaust gas purification
device. In this case, as such an exhaust gas purification device, there can be exemplified
a NOx storage reduction catalyst (hereinafter referred to as a NOx catalyst), a particulate
filter (hereinafter referred to as a filter) with a catalyst carried thereon, one
having these NOx catalyst and filter in combination, and so on.
[0003] In addition, a reducing agent addition valve for adding a reducing agent to an exhaust
gas may be further arranged in the exhaust passage at a location upstream of the precatalyst.
In this case, when the exhaust gas purification device is raised in temperature or
the air fuel ratio of an ambient atmosphere of the exhaust gas purification device
is decreased, so as to recover the function of the exhaust gas purification device,
the reducing agent is added to the exhaust gas by the reducing agent addition valve,
whereby the reducing agent is supplied to the precatalyst and the exhaust gas purification
device.
[0004] Japanese patent application laid-open No.
2005-127257 describes a technique in which a reforming catalyst for reforming the fuel supplied
is arranged in an exhaust passage at an upstream side of a NOx catalyst. Further,
Japanese patent application laid-open No.
2005-127257 describes a technique in which a reforming catalyst is disposed in a central portion
of an exhaust passage, and a bypass circuit through which an exhaust gas flows is
formed on an outer periphery of the reforming catalyst.
WO 2002/33231 relates to an exhaust treatment unit with a catalyst arrangement, comprising a storage
catalyst DISCLOSURE OF THE INVENTION
[0005] In case where the position in which a reducing agent addition valve is disposed in
an exhaust passage is a position in which at least part of a reducing agent added
to an exhaust gas reaches a precatalyst in the state of liquid, the reducing agent
having reached the precatalyst in the liquid state vaporizes in the precatalyst. Then,
a part of the reducing agent thus vaporized is oxidized in the precatalyst, but the
remaining reducing agent having not been oxidized is supplied to an exhaust gas purification
device.
[0006] The present invention has for its object to provide a technique in which in case
where a reducing agent addition valve is arranged in a position in which at least
part of a reducing agent added to an exhaust gas in an exhaust passage at a location
upstream of a precatalyst reaches the precatalyst in the state of liquid, it is possible
to supply the reducing agent in a more suitable state to an exhaust gas purification
device which is arranged in the exhaust passage at a location downstream of the precatalyst.
[0007] In the present invention, when the addition of the reducing agent is performed by
the reducing agent addition valve, the flow rate of the exhaust gas flowing into the
precatalyst is decreased so that at least part of the reducing agent, which has reached
the precatalyst and has vaporized in the precatalyst, is caused to flow back.
[0008] More specifically, an exhaust gas purification system for an internal combustion
engine according to the present invention is characterized by including:
an exhaust gas purification device that is arranged in an exhaust passage of the internal
combustion engine and is constructed to include a catalyst;
a precatalyst that is arranged in the exhaust passage at a location upstream of said
exhaust gas purification device and has an oxidation function;
a reducing agent addition valve that is arranged in the exhaust passage at a location
upstream of said precatalyst and adds a reducing agent to an exhaust gas when the
reducing agent is supplied to said precatalyst and said exhaust gas purification device;
and
an exhaust gas flow rate control means that controls a flow rate of the exhaust gas
flowing into said precatalyst;
wherein said reducing agent addition valve is disposed in a position in which at least
part of the reducing agent added to the exhaust gas reaches said precatalyst in the
state of liquid, and
wherein when the addition of the reducing agent is performed by said reducing agent
addition valve, said exhaust gas flow rate control means decreases the flow rate of
the exhaust gas flowing into said precatalyst so that at least part of the reducing
agent, which has reached said precatalyst and has vaporized in said precatalyst, is
caused to flow back.
[0009] The volume of the reducing agent having reached the precatalyst in the state of liquid
expands upon vaporization thereof in the precatalyst. A flow of the reducing agent
in a direction opposite to the flow direction of the exhaust gas is caused to generate
due to this expansion. As a result, it is possible to cause a part of the vaporized
reducing agent to flow back by decreasing the flow rate of the exhaust gas flowing
into the precatalyst at the time when the addition of the reducing agent is performed
by the reducing agent addition valve.
[0010] Once the reducing agent having reached the precatalyst flows back, the time taken
until said reducing agent reaches the exhaust gas purification device becomes longer
as compared with the case in which no backflow has been generated. As a result, said
reducing agent is more easily mixed with the exhaust gas until the time when the reducing
agent reaches the exhaust gas purification device. In addition, the period during
which the reducing agent is supplied to the exhaust gas purification device can be
made longer. Thus, according to the present invention, the reducing agent can be supplied
to the exhaust gas purification device in a more suitable state.
[0011] In the present invention, when the addition of the reducing agent is performed by
the reducing agent addition valve, the exhaust gas flow rate control means may control
the flow rate of the exhaust gas so that the flow rate of the exhaust gas flowing
into the precatalyst becomes smaller than the expansion rate of the reducing agent
when the reducing agent having reached the precatalyst is vaporized to expand in the
precatalyst.
[0012] According to this, it is possible to cause at least part of the reducing agent having
been vaporized in the precatalyst to flow back.
[0013] In the present invention, when the exhaust gas purification device is raised in temperature,
the reducing agent may be added to the exhaust gas by means of the reducing agent
addition valve.
[0014] The reducing agent added from the reducing agent addition valve is oxidized in the
precatalyst and the catalyst that is contained in the exhaust gas purification device.
In the present invention, the reducing agent not oxidized in the precatalyst is supplied
to the exhaust gas purification device in a state better mixed with the exhaust gas
over a longer period of time. Therefore, the oxidation of the reducing agent in the
catalyst contained in the exhaust gas purification device can be more facilitated.
Accordingly, the temperature raising property of the exhaust gas purification device
can be improved.
[0015] In the present invention, in case where the exhaust gas purification device is constructed
to include a NOx catalyst, the reducing agent can be added to the exhaust gas by means
of the reducing agent addition valve when NOx or SOx stored in the NOx catalyst is
released and reduced.
[0016] In this case, the air fuel ratio of an ambient atmosphere of the NOx catalyst can
be lowered over a longer period of time. Accordingly, it is possible to facilitate
the release and reduction of NOx or SOx occluded in the NOx catalyst in a more efficient
manner.
[0017] In the present invention, provision may be further made for a bypass passage that
has one end thereof connected to the exhaust passage at a location upstream of the
reducing agent addition valve and the other end thereof connected to the exhaust passage
at a location downstream of the exhaust gas purification device, and a bypass control
valve that controls the flow rate of the exhaust gas flowing in the bypass passage.
[0018] In the case of provision of the bypass passage and the bypass control valve as described
above, the exhaust gas flow rate control means may decrease the flow rate of the exhaust
gas flowing into the precatalyst by increasing the flow rate of the exhaust gas flowing
in the bypass passage by means of the bypass control valve.
[0019] In case where the flow rate of the exhaust gas flowing into the precatalyst is decreased
by increasing the flow rate of the exhaust gas flowing in the bypass passage when
the reducing agent is added from the reducing agent addition valve, there is a fear
that if the flow rate of the exhaust gas flowing in the bypass passage is increased
over a long period of time, the reducing agent, which has been vaporized in the precatalyst
and has flown back, might flow into the bypass passage from the one end thereof.
[0020] Accordingly, in the case of increasing the flow rate of the exhaust gas flowing in
the bypass passage by means of the bypass control valve, the flow rate of the exhaust
gas flowing in the bypass passage may be temporarily increased at the time when the
reducing agent is added from the reducing agent addition valve, and at the same time,
the flow rate of the exhaust gas flowing in the bypass passage may be controlled to
be substantially zero by means of the bypass control valve immediately after the addition
of the reducing agent. According to such control, when the reducing agent is added
from the reducing agent addition valve, the flow rate of the exhaust gas flowing into
the precatalyst can be decreased, and at the same time, it is possible to suppress
the reducing agent having flown back from coming into the bypass passage.
[0021] In addition, in the case of provision of the bypass passage and the bypass control
valve as stated above, when the flow rate of the exhaust gas flowing into the precatalyst
is decreased by means of the exhaust gas flow rate control means, the flow rate of
the exhaust gas flowing into the precatalyst may be controlled to such an extent that
the reducing agent having been vaporized in the precatalyst and having flown back
does not reach a connecting portion of the exhaust passage to which the one end of
the bypass passage is connected. With such control, too, it is possible to suppress
the reducing agent having flown back from coming into the bypass passage.
[0022] Moreover, in the present invention, even in the case of provision of the bypass passage
and the bypass control valve, the exhaust gas flow rate control means may decrease
the flow rate of the exhaust gas flowing into the precatalyst according to a method
other than increasing the flow rate of the exhaust gas flowing in the bypass passage.
[0023] In this case, when the exhaust gas flow rate control means decreases the flow rate
of the exhaust gas flowing into the precatalyst, the flow rate of the exhaust gas
flowing in the bypass passage may be controlled to be substantially zero by means
of the bypass control valve. According to such control, it is possible to suppress
the reducing agent having flown back from coming into the bypass passage.
[0024] In the present invention, the precatalyst may be formed in such a manner that the
exhaust gas flows between an outer peripheral surface of the precatalyst and an inner
peripheral surface of the exhaust passage. In this case, the amount of exhaust gas
flowing into the precatalyst is originally smaller as compared with the case in which
the entire exhaust gas flowing into the exhaust gas purification device passes through
the precatalyst. Therefore, when the reducing agent reaches the precatalyst and is
vaporized to expand therein, a backflow of the reducing agent is liable to be generated.
In addition, in this case, a part of the reducing agent, which has been vaporized
in the precatalyst and has flown back, is supplied to the exhaust gas purification
device while passing between the outer peripheral surface of the precatalyst and the
inner peripheral surface of the exhaust passage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025]
Fig. 1 is a first view showing the schematic construction of intake and exhaust systems
of an internal combustion engine according to an embodiment of the present invention.
Fig. 2 is a graph showing the change of an air fuel ratio of an exhaust gas flowing
into a filter at the time when fuel has been added from a fuel addition valve according
to the embodiment of the present invention.
Fig. 3 is a first flow chart illustrating a routine for filter regeneration control
according to the embodiment of the present invention.
Fig. 4 is a second flow chart illustrating a routine for filter regeneration control
according to the embodiment of the present invention.
Fig. 5 is a second view showing the schematic construction of intake and exhaust systems
of an internal combustion engine according to the embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0026] Hereinafter, a specific preferred embodiment of an exhaust gas purification system
for an internal combustion engine according to the present invention will be described
while referring to the accompanying drawings.
(Embodiment 1)
<Schematic Construction of Intake and Exhaust Systems in an Internal Combustion Engine>
[0027] Here, reference will be made, by way of example, to a case where the present invention
is applied to a diesel engine used for driving a vehicle. Fig. 1 is a view that shows
the schematic construction of intake and exhaust systems of an internal combustion
engine according to an embodiment of the present invention.
[0028] The internal combustion engine 1 is a diesel engine for driving a vehicle. An intake
passage 3 and an exhaust passage 2 are connected with the internal combustion engine
1. A throttle valve 7 and an air flow meter 8 are arranged in the intake passage 3.
[0029] A filter 5 for collecting particulate matter (hereinafter referred to as PM) in an
exhaust gas is arranged in the exhaust passage 2. A NOx catalyst 9 is carried by the
filter 5. In this embodiment, the filter 5 and the NOx catalyst 9 together correspond
to an exhaust gas purification device of the present invention.
[0030] An oxidation catalyst 4 is arranged in the exhaust passage 2 at a location upstream
of the filter 5. Here, note that in this embodiment, the oxidation catalyst 4 corresponds
to a precatalyst according to the present invention. Here, note that the oxidation
catalyst 4 need only be a catalyst having an oxidation function, and may be, for example,
a three way catalyst, a NOx catalyst or the like.
[0031] A fuel addition valve 6 for adding a reducing agent in the form of fuel to the exhaust
gas is arranged in the exhaust passage 2 at an upstream side of the oxidation catalyst
4. The fuel addition valve 6 is disposed in proximity to the oxidation catalyst 4
with its fuel injection hole through which fuel is injected being in opposition to
an upstream end face of the oxidation catalyst 4. Fuel is injected from the fuel injection
hole of the fuel addition valve 6 in a conical shape (in Fig. 1, a hatched portion
denotes the atomization of fuel). At least part of the fuel thus injected reaches
the oxidation catalyst 4 in the state of liquid. In this embodiment, the fuel addition
valve 6 corresponds to a reducing agent addition valve.
[0032] In this embodiment, an EGR passage 15 is arranged to introduce a part of the exhaust
gas into the internal combustion engine 1 as an EGR gas. The EGR passage 15 has one
end thereof connected to the exhaust passage 2 at an upstream side of the fuel addition
valve 6, and the other end thereof connected to the intake passage 3 at a downstream
side of the throttle valve 7. An EGR valve 16 for controlling the flow rate of the
EGR gas is arranged in the EGR passage 15.
[0033] Further, in this embodiment, a bypass passage 17 is provided through which the exhaust
gas flows bypassing the oxidation catalyst 4 and the filter 5. The bypass passage
17 has one end thereof connected to the exhaust passage 2 at the upstream side of
the fuel addition valve 6, and the other end thereof connected to the exhaust passage
2 at a downstream side of the filter 5. A bypass control valve 18 for controlling
the flow rate of the exhaust gas flowing in the bypass passage 17 is arranged in the
bypass passage 17.
[0034] An air fuel ratio sensor 13 for detecting the air fuel ratio of the exhaust gas is
arranged in the exhaust passage 2 between the oxidation catalyst 4 and the filter
5. In addition, a temperature sensor 14 for detecting the temperature of the exhaust
gas is arranged in the exhaust passage 2 at a downstream side of the filter 5.
[0035] An electronic control unit (ECU) 10 for controlling the internal combustion engine
1 is provided in conjunction with the internal combustion engine 1 as constructed
in the above-described manner. The air flow meter 8, the air fuel ratio sensor 13,
the temperature sensor 14, a crank position sensor 11, and an accelerator opening
sensor 12 are electrically connected to the ECU 10. The output signals of these sensors
and meter are input to the ECU 10.
[0036] The crank position sensor 11 is a sensor that detects the crank angle of the internal
combustion engine 1. The accelerator opening sensor 12 is a sensor that detects the
degree of accelerator opening of the vehicle on which the internal combustion engine
1 is installed. The ECU 10 calculates the number of revolutions per minute of the
internal combustion engine 1(hereinafter simply referred to as the engine rotation
number) based on the output value of the crank position sensor 11, and also calculates
the load of the internal combustion engine 1 based on the output value of the accelerator
opening sensor 12. In addition, the ECU 10 estimates the air fuel ratio of the ambient
atmosphere of the filter 5 (i.e., the ambient atmosphere of the NOx catalyst 9) based
on the output value of the air fuel ratio sensor 13, and also estimates the temperature
of the filter 5 (i.e. , the temperature of the NOx catalyst 9) based on the output
value of the temperature sensor 14.
[0037] Also, the throttle valve 7, the fuel addition valve 6, the EGR valve 16, the bypass
control valve 18 and fuel injection valves of the internal combustion engine 1 are
electrically connected to the ECU 10. These valves are controlled by the ECU 10.
<Filter Regeneration Control>
[0038] In this embodiment, filter regeneration control is performed to remove the PM collected
in the filter 5. The filter regeneration control according to this embodiment is achieved
by adding fuel from the fuel addition valve 6 thereby to supply the fuel to the oxidation
catalyst 4 and the filter 5. When the fuel supplied to the oxidation catalyst 4 is
oxidized in the oxidation catalyst 4, the exhaust gas flowing into the filter 5 is
raised in temperature by the heat of oxidation generated. As a result, the temperature
of the filter 5 is raised. In addition, fuel having passed the oxidation catalyst
4 without being oxidized therein is supplied to the filter 5. When the fuel supplied
to the filter 5 is oxidized in the NOx catalyst 9, the filter 5 is further raised
in temperature by means of the oxidation heat. The temperature of the filter 5 can
be raised to a temperature at which the oxidation of the PM therein is possible, by
controlling the amount of fuel added from the fuel addition valve 6, as a result of
which the PM collected in the filter 5 can be removed by the oxidation thereof.
[0039] In this embodiment, when the filter regeneration control is carried out, the control
to decrease the flow rate of the exhaust gas flowing into the oxidation catalyst 4
is performed. As stated above, in this embodiment, at least part of the fuel added
from the fuel addition valve 6 reaches the oxidation catalyst 4 in the state of liquid.
The fuel having reached the oxidation catalyst 4 in the state of liquid is vaporized
by the heat of oxidation generated in the oxidation catalyst 4. As the fuel in the
liquid state is vaporized, the volume of the fuel expands.
[0040] At this time, when the flow rate of the exhaust gas flowing into the oxidation catalyst
4 is smaller than the speed or rate of expansion of the fuel, there occurs a backflow
in the oxidation catalyst 4 in which at least a part of the vaporized fuel flows in
a direction opposite to the direction in which the exhaust gas flows. Addition, a
part of the fuel having been vaporized and having flown back in the oxidation catalyst
4 once flows out from the upstream end face of the oxidation catalyst 4, and thereafter
flows again into the oxidation catalyst 4 along with the exhaust gas. That which has
not been oxidized in the oxidation catalyst 4, among the fuel once having flown back
in the oxidation catalyst 4 and the fuel once having flown out from the upstream end
face of the oxidation catalyst 4 and again having flown into the oxidation catalyst
4, flows out from a downstream end face of the oxidation catalyst 4 together with
the exhaust gas, and is supplied to the filter 5.
[0041] Once the fuel having reached the oxidation precatalyst 4 flows back, the time taken
until the fuel reaches the filter 5 becomes longer as compared with the case in which
no backflow has been generated. As a result, the fuel is more easily mixed with the
exhaust gas during the time until when the fuel reaches the filter 5. In addition,
as shown in Fig. 2, when the fuel having reached the oxidation catalyst 4 once flows
back, it is possible to make longer the period during which fuel is supplied to the
filter 5.
[0042] Fig. 2 is a graph showing the change of the air fuel ratio of the exhaust gas flowing
into the filter 5 at the time when fuel has been added from the fuel addition valve
6. In Fig. 2, the axis of ordinate denotes the air fuel ratio A/F of the exhaust gas
flowing into the filter 5, and the axis of abscissa denotes time t. In addition, curve
L1 denotes a case where the backflow of the fuel having reached the oxidation catalyst
4 is not generated, and curve L2 denotes a case where the fuel having reached the
oxidation catalyst 4 once flows back. As shown in Fig. 2, in case where the fuel having
reached the oxidation catalyst 4 once flows back, the period in which the air fuel
ratio of the exhaust gas flowing into the filter 5 becomes low is longer as compared
with the case in which there occurs no backflow of fuel. In other words, it can be
determined that the period in which fuel is supplied to the filter 5 is long.
[0043] As described above, fuel can be supplied to the filter 5 in a more suitable state
by causing the fuel having reached the oxidation catalyst 4 and having been vaporized
therein to flow back. Accordingly, in this embodiment, by performing the control to
increase the flow rate of exhaust gas when filter regeneration control is carried
out, the flow rate of the exhaust gas flowing into the oxidation catalyst 4 is made
smaller than the speed or rate of expansion at which fuel is vaporized to expand in
the oxidation catalyst 4.
[0044] Here, reference will be made to a routine for filter regeneration control according
to this embodiment based on a flow chart shown in Fig. 3. This routine is beforehand
stored in the ECU 10, and is repeatedly executed at a specified time interval during
the operation of the internal combustion engine.
[0045] In this routine, first in step S101, the ECU 10 determines whether an execution condition
for filter regeneration control holds. Here, note that when the amount of collection
of the PM in the filter 5 becomes equal to or more than a predetermined amount of
collection, it may be determined that the execution condition of filter regeneration
control holds. The amount of collection of the PM in the filter 5 can be estimated
from the history of the operating condition of the internal combustion engine 1 or
the like. When a positive determination is made in S101, the ECU 10 advances to S102,
whereas when a negative determination is made, the ECU 10 once terminates the execution
of this routine.
[0046] In S102, the ECU 10 calculates the temperature Tcco of the oxidation catalyst 4 based
on the operating condition of the internal combustion engine 1 or the like. Here,
note that a temperature sensor may be arranged in the exhaust passage 2 immediately
downstream of the oxidation catalyst 4, so that the temperature Tcco of the oxidation
catalyst 4 can be estimated based on the detected value of the temperature sensor.
[0047] Then, the ECU 10 proceeds to step S103, where an amount of fuel Qfadd to be added
from the fuel addition valve 6 required to raise the temperature of the filter 5 up
to a target temperature in the filter regeneration control is calculated. The amount
of fuel to be added Qfadd can be calculated based on a difference between the current
temperature of the filter 5 and the target temperature, the operating condition of
the internal combustion engine 1, and the temperature Tcco of the oxidation catalyst
4.
[0048] Thereafter, the ECU 10 proceeds to step S104, where the expansion rate Vfex of the
fuel is calculated at the time when the fuel having been added from the fuel addition
valve 6 and having reached the oxidation catalyst 4 in the state of liquid is vaporized
to expand in the oxidation catalyst 4. The expansion rate Vfex of the fuel can be
calculated based on the temperature Tcco of the oxidation catalyst 4 and the amount
of fuel being added Qfadd.
[0049] Subsequently, the ECU 10 proceeds to step S105, where a target flow rate of exhaust
gas Vgast is set which is a target value of the flow rate of the exhaust gas flowing
into the oxidation catalyst 4 when exhaust gas flow rate decreasing control is performed
in S106 to be described latter. At this time, the target flow rate of exhaust gas
Vgast is set to a value that is smaller than the expansion rate Vfex of the fuel calculated
in S104.
[0050] Then, the ECU 10 proceeds to step S106, where the flow rate of the exhaust gas flowing
into the oxidation catalyst 4 is decreased to the target flow rate of exhaust gas
Vgast by performing the exhaust gas flow rate decreasing control.
[0051] Here, as the exhaust gas flow rate decreasing control, there can be exemplified the
control to decrease the amount of intake air of the internal combustion engine 1 by
means of the throttle valve 7, the control to increase the amount of EGR gas by means
of the EGR valve 16, the control to increase the flow rate of the exhaust gas flowing
through the bypass passage 17 by means of the bypass control valve 18, and so on.
When the amount of intake air in the internal combustion engine 1 is decreased, the
flow rate of the exhaust gas in the internal combustion engine 1 is decreased, so
the flow rate of the exhaust gas flowing into the oxidation catalyst 4 is consequentially
decreased, too. In addition, when the amount of EGR gas is increased, the flow rate
of the exhaust gas flowing through the exhaust passage 2 at the downstream side of
its connecting portion with the EGR passage 15 is decreased, so the flow rate of the
exhaust gas flowing into the oxidation catalyst 4 is decreased. Moreover, when the
flow rate of the exhaust gas flowing through the bypass passage 17 is increased, the
flow rate of the exhaust gas flowing through the exhaust passage 2 at the downstream
side of its connecting portion with one end of the bypass passage 17 is decreased,
so the flow rate of the exhaust gas flowing into the oxidation catalyst 4 is decreased.
The exhaust gas flow rate control according to this embodiment can be achieved by
either one of these control schemes or by any combination of these control schemes.
In this embodiment, the ECU 10 executing the S106 corresponds to an exhaust gas flow
rate control means according to the present invention.
[0052] Subsequently, ECU 10 proceeds to S107, where it performs filter regeneration control
by executing the addition of fuel from the fuel addition valve 6. Thereafter, the
ECU 10 once terminates the execution of this routine.
[0053] According to the routine as stated above, the addition of fuel by means of the fuel
addition valve 6 is carried out in a state where the flow rate of the exhaust gas
flowing into the oxidation catalyst 4 is smaller than the expansion rate of vaporized
fuel at the time when fuel is vaporized to expand in the oxidation catalyst 4. Therefore,
when fuel reaches the oxidation catalyst 4 and is vaporized therein, there occurs
a backflow of the fuel.
[0054] Accordingly, fuel can be supplied to the filter 5 in a more suitable manner. As a
result, the oxidation of fuel in the NOx catalyst 9 carried by the filter 5 becomes
liable to be facilitated. With this, the raising of the temperature of the filter
5, in particular, that of the upstream end face of the filter 5, can be improved,
and so the temperature of the filter 5 can be raised up to the target temperature
more quickly. In addition, the adhesion of fuel to the filter 5 can be suppressed.
Further, fuel can be suppressed from passing through the filter 5 without being oxidized
in the NOx catalyst 9.
[0055] Here, note that in this embodiment, if the fuel reaches up to the connecting portion
of the exhaust passage 2 with the one end of the bypass passage 17 and flows into
the bypass passage 17 at the time when the backflow of the vaporized fuel has occurred
in the oxidation catalyst 4, the fuel might be discharged to the outside. Accordingly,
in this embodiment, in case where the exhaust gas flow rate decreasing control is
carried out by increasing the flow rate of the exhaust gas flowing through the bypass
passage 17, the degree of opening of the bypass control valve 18 may be caused to
temporarily increase in synchronization with the addition of fuel from the fuel addition
valve 6, and immediately thereafter, the bypass passage 17 may be interrupted by the
bypass control valve 18.
[0056] According to this, when fuel is added from the fuel addition valve 6, the flow rate
of the exhaust gas flowing through the bypass passage 17 is temporary increased, and
immediately thereafter the flow rate of the exhaust gas flowing through the bypass
passage 17 becomes substantially zero. Accordingly, at the time when fuel is added
from the fuel addition valve 6, it is possible to decrease the flow rate of the exhaust
gas flowing into the oxidation catalyst 4, and at the same time it is possible to
suppress the fuel having flown back from coming into the bypass passage. As a result,
it is possible to suppress fuel from being discharged to the outside.
[0057] In addition, in this embodiment, when the target flow rate of exhaust gas Vgast is
set, the target flow rate of exhaust gas Vgast may be set to such a value that the
fuel having been vaporized in the oxidation catalyst 4 and having flown back does
not reach up to the connecting portion of the exhaust passage 2 with the one end of
the bypass passage 17. Such a target flow rate of exhaust gas Vgast can be calculated
based on a distance from the connecting portion of the exhaust passage 2 with the
one end of the bypass passage 17 to the oxidation catalyst 4 and the expansion rate
Vfex of the fuel. According to this, too, it is possible to suppress the fuel having
flown back from coming into the bypass passage 17.
[0058] Moreover, in this embodiment, the exhaust gas flow rate decreasing control may be
carried out by other control methods or schemes than the control to increase the flow
rate of the exhaust gas flowing through the bypass passage 17. Hereinafter, reference
will be made to a routine for filter regeneration control in this case based on a
flow chart shown in Fig. 4. Here, note that this routine is the routine shown in Fig.
3 with step S206 added thereto. Therefore, only step S206 will be explained, while
omitting an explanation of the other steps. This routine is beforehand stored in the
ECU 10, and is repeatedly executed at a specified time interval during the operation
of the internal combustion engine.
[0059] In this routine, the ECU 10 proceeds to S206 after S105. In S206, the ECU 10 closes
the bypass control valve 18 thereby to interrupt the bypass passage 17. Thereafter,
the ECU 10 proceeds to S106. In this case, in S106, the ECU 10 executes the exhaust
gas flow rate decreasing control according to a control method or scheme other than
the control to increase the flow rate of the exhaust gas flowing through the bypass
passage 17, so that the flow rate of the exhaust gas flowing into the oxidation catalyst
4 is decreased to the target flow rate of exhaust gas Vgast.
[0060] According to such a routine, when fuel is added from the fuel addition valve 6, the
flow rate of the exhaust gas flowing through the bypass passage 17 becomes substantially
zero. Accordingly, it is possible to suppress the fuel having been vaporized in the
oxidation catalyst 4 and having flown back from coming into the bypass passage.
[0061] The oxidation catalyst 4 according to this embodiment may have an outer diameter
which is smaller than an inner diameter of the exhaust passage 2, as shown in Fig.
5. In other words, the sectional area of the oxidation catalyst 4 in a direction perpendicular
to the direction in which the exhaust gas flows may be smaller than the sectional
area of the exhaust passage 2 in a direction perpendicular to the direction in which
the exhaust gas flows. In the case of such a construction, the exhaust gas flows between
an outer peripheral surface of the oxidation catalyst 4 and an inner peripheral surface
of the exhaust passage 2. In addition, in such a construction, the fuel addition valve
6 and the oxidation catalyst 4 are arranged in such a manner that when fuel is injected
from the fuel injection hole of the fuel addition valve 6, the upstream end face of
the oxidation catalyst 4 is positioned in the midst of atomization of the fuel formed
in a conical shape (in Fig. 5, a hatched portion denotes the atomization of the fuel).
[0062] In the case of the above-mentioned construction, the amount of exhaust gas flowing
into the oxidation catalyst 4 is originally smaller as compared with the case in which
the entire exhaust gas flowing into the filter 5 passes through the oxidation catalyst
4. Therefore, when fuel reaches the oxidation catalyst 4 and is vaporized to expand
therein, a backflow of the fuel is liable to be generated.
[0063] In this embodiment, the description has been made by taking as an example the case
where the fuel addition valve 6 is disposed in proximity to the oxidation catalyst
4 with its fuel injection hole being in opposition to the upstream end face of the
oxidation catalyst 4. However, the fuel addition valve 6 may be arranged in any position
as long as at least part of the fuel added from the fuel addition valve 6 reaches
the oxidation catalyst 4 in the state of liquid.
[0064] Further, in this embodiment, when NOx reduction control to release and reduce the
NOx stored in the NOx catalyst 9 or SOx poisoning recovery control to release and
reduce the SOx stored in the NOx catalyst 9 is performed, the exhaust gas flow rate
decreasing control may be carried out, similar to when the filter regeneration control
is performed.
[0065] In the NOx reduction control, the addition of fuel by means of the fuel addition
valve 6 is performed so as to lower the air fuel ratio of the ambient atmosphere of
the NOx catalyst 9. Also, in the SOx poisoning recovery control, the addition of fuel
by means of the fuel addition valve 6 is performed so as to raise the temperature
of the NOx catalyst 9 and at the same time to lower the air fuel ratio of the ambient
atmosphere of the NOx catalyst 9.
[0066] As stated above, by generating the backflow of the fuel vaporized in the oxidation
catalyst 4 by performing the exhaust gas flow rate decreasing control according to
this embodiment when the addition of fuel is performed by means of the fuel addition
valve 6, fuel can be supplied to the NOx catalyst 9 in a state better mixed with the
exhaust gas, and at the same time, the air fuel ratio of the ambient atmosphere of
the NOx catalyst 9 can be lowered over a longer period of time. Accordingly, by performing
the exhaust gas flow rate decreasing control upon execution of the NOx reduction control
or the SOx poisoning recovery control, the release and reduction of NOx or SOx can
be more facilitated. In addition, the adhesion of fuel to the filter 5 (the NOx catalyst
9) can be suppressed. Further, fuel can be suppressed from passing through the filter
5 without being oxidized in the NOx catalyst 9.
INDUSTRIAL APPLICABILITY
[0067] According to the present invention, in case where a reducing agent addition valve
is arranged in a position in which at least part of a reducing agent added to an exhaust
gas in an exhaust passage at a location upstream of a precatalyst reaches the precatalyst
in the state of liquid, it is possible to supply the reducing agent to the exhaust
gas purification device, which is arranged in the exhaust passage at a location downstream
of the precatalyst, in a more suitable manner.
1. Ein Abgasreinigungssystem für einen Verbrennungsmotor (1), das aufweist:
eine Abgasreinigungsvorrichtung (5), die in einem Abgaskanal (2) des Verbrennungsmotors
vorgesehen ist und konstruiert ist, um einen Katalysator (9) aufzuweisen,
einen Vorkatalysator (4), der in dem Abgaskanal an einem Ort stromaufwärts von der
Abgasreinigungsvorrichtung angeordnet ist und eine Oxidierfunktion hat,
ein Reduziermittelzuführventil (6), das in dem Abgaskanal an einem Ort stromaufwärts
von dem Vorkatalysator angeordnet ist und einem Abgas ein Reduziermittel zuführt,
wenn das Reduziermittel dem Vorkatalysator und der Abgasreinigungsvorrichtung zugeführt
wird, und
eine elektronische Steuereinheit (10), die eine Strömungsrate des Abgases, das in
den Vorkatalysator strömt, steuert,
wobei das Reduziermittelzuführventil in einer Position angeordnet ist, in der zumindest
ein Teil des Reduziermittels, das dem Abgas zugeführt wurde, den Vorkatalysator in
flüssigem Zustand erreicht, und
wobei, wenn die Zuführung des Reduziermittels durch das Reduziermittelzuführventil
ausgeführt wird, die elektronische Steuereinheit angeordnet ist, um zumindest einen
Teil des Reduziermittels, das den Vorkatalysator erreicht hat und in dem Vorkatalysator
verdampft ist, zu veranlassen zurückzuströmen, indem die Strömungsrate des Abgases
gesteuert wird, so dass die Strömungsrate des Abgases, das in den Vorkatalysator strömt,
kleiner als eine Expansionsrate des Reduziermittels wird, wenn das Reduziermittel,
das den Vorkatalysator erreicht hat, verdampft ist, um in dem Vorkatalysator zu expandieren.
2. Das Abgasreinigungssystem für einen Verbrennungsmotor nach Anspruch 1, wobei das Reduziermittelzuführventil
(6) angeordnet ist, um das Reduziermittel dem Abgas zuzuführen, wenn die Temperatur
der Abgasreinigungsvorrichtung (5) erhöht wird.
3. Abgasreinigungssystem für einen Verbrennungsmotor nach Anspruch 1,
wobei die Abgasreinigungsvorrichtung (5) konstruiert ist, um einen NOx-Speicherreduzierkatalysator
(9) aufzuweisen, und
wobei, wenn verursacht wird, dass das Freigeben und Reduzieren von NOx oder SOx, das
in dem NOx-Speicherreduzierkatalysator gespeichert ist, freigegeben und reduziert
wird, das Reduziermittelzuführventil (6) das Reduziermittel dem Abgas zufügt.
4. Abgasreinigungssystem für einen Verbrennungsmotor nach einem der Ansprüche 1 bis 3,
das ferner aufweist:
einen Bypasskanal (17), dessen eines Ende mit dem Abgaskanal (2) an einem Ort stromaufwärts
des Reduziermittelzuführventils (6) verbunden ist und dessen anderes Ende mit dem
Abgaskanal an einem Ort stromabwärts der Abgasreinigungsvorrichtung (5) verbunden
ist, und
ein Bypasssteuerventil (18), das die Strömungsrate des durch den Bypasskanal strömenden
Abgases steuert,
wobei die elektronische Steuereinheit angeordnet ist, um die Strömungsrate des den
Vorkatalysator strömenden Abgases zu verringern, indem die Strömungsrate des durch
den Bypasskanal strömenden Abgases mittels des Bypasssteuerventils erhöht wird.
5. Abgasreinigungssystem für einen Verbrennungsmotor nach Anspruch 4, wobei die elektronische
Steuereinheit (10) angeordnet ist, um die Strömungsrate des in den Vorkatalysator
(4) strömenden Abgases zu verringern, indem die Strömungsrate des durch den Bypasskanal
strömenden Abgases mittels des Bypasssteuerventils (18) zeitweise erhöht wird und
unmittelbar danach die Strömungsrate des durch den Bypasskanal strömenden Abgases
mittels des Bypasssteuerventils steuert, um im Wesentlichen Null zu sein, wenn das
Reduziermittel von dem Reduziermittelzuführventil zugefügt wird.
6. Abgasreinigungssystem für einen Verbrennungsmotor nach einem der Ansprüche 1 bis 5,
wobei der Vorkatalysator (4) in einer solchen Weise ausgebildet ist, dass das Abgas
zwischen einer Außenumfangsfläche des Vorkatalysators und einer Innenumfangsfläche
des Abgaskanals (2) strömt.